The present invention relates generally to sewing machine heads and more particularly to those of the convertible-bed type or the type having a bed structure adapted to form a so-called flat-table type bed or a so-called free-arm type bed as desired in use for the form of fabric to be worked.
As is well known, sewing machine beds are generally classified into two types, flat-table and free-arm. Flat-table type beds have a work table portion with a needle plate mounted thereon and which extends under the entire overhead arm of the machine head to define a wide, flat work-supporting surface. In contrast, free-arm type beds are tubular in form, extending horizontally from one side of the vertical column of the machine head substantially in parallel with the overhead arm thereof for convenience in sewing sleeves or other work fabrics of tubular form. In the past, sewing machines have usually been formed with a bed of one or the other of the two different types. It is highly desirable, however, to provide on a single sewing machine a bed structure capable of serving as a flat-table type bed and also as a free-arm type one and various forms of sewing machines have previously been proposed which have a bed structure convertible or usable in two ways, as a flat-table type and a free-arm type bed.
Conventional forms of convertible-bed type sewing machine have actually been of the so-called free-arm type, including a tubular or free-arm type bed extending horizontally from one side of the vertical column of the machine head and a bed attachment or an auxiliary bed member which is udapted to be detachably fitted to the tubular bed with a slot formed to fittingly receive the latter and has a top surface formed to serve as a continuation of the elongate work-supporting top surface of the tubular or free-arm bed. Such sewing machines are usable as a flat-table type machine with the auxiliary table member fitted around the free-arm bed and, for sewing tubular fabrics, are used as a free-arm bed type machine with the auxiliary table member removed from the machine head. In sewing various forms of work fabric with such conventional machines, it has been necessary to attach and detach the auxiliary table member from time to time involving substantial loss of labor and time.